1. Field of the Invention
The present invention relates to a process for the purification of hydrochloric acid. Particularly, the present process relates to a process for the purification of hydrochloric acid containing hydrogen fluoride, which process comprises treating hydrochloric acid with at least one silicon compound.
2. Description of the Related Art
When a chlorofluorohydrocarbon is produced through fluorination of a chlorohydrocarbon with hydrogen fluoride, an equimolar amount of hydrogen chloride with consumed hydrogen fluoride is by-produced. Also, when tetrafluoroethylene is produced through thermal decomposition of chlorodifluoromethane, an equimolar amount of hydrogen chloride with decomposed chlorodefluoromethane is by-produced. Such hydrogen chloride is utilized as the by-product hydrochloric acid, but it contains fluorides such as hydrogen fluoride and silicon fluoride as impurities. Since the fluorides are not desired for effective utilization of the by-product hydrochloric acid, it is very important to remove them.
A number of processes have been proposed to remove the fluorides from hydrochloric acid containing them. For example, U.S. Pat. No. 3,411,879 and Japanese Patent Kokai Publication No. 110999/1975 describe processes for the purification of hydrochloric acid comprising removal of fluorine ions with silica gel. However, these processes are not suitable for effective purification of hydrochloric acid containing hydrogen fluoride in a high concentration.
Japanese Patent Kokai Publication No. 223604/1983 describes a process for the purification of hydrochloric acid containing hydrogen fluoride by contacting hydrochloric acid with a silicon compound. In this process, a large amount of an expensive trialkylchlorosilane compound should be used. In addition, it takes a relatively long time to react the by-produced silicon compound mixture comprising a hexaalkyldisiloxane compound as a main component even at a high temperature in order to reuse the silicon compound mixture.
It is found that it takes about five days to purify the silicon compound mixture without stirring at room temperature and takes 150 minutes with stirring at 90.degree. C.